Method for locating tension failures in oil well casings



July 23. 1968 c. E, MURPHEY, JR, ET AL 3,393,732

METHOD FOR LOCATING TENSION FAILURES IN OIL WELL CASINGS Filed May 21, 1965 AMPLIFIER uon-mmnsnc 40 42 36 MAGNETlC M 4 MAGNETIC 45 25 MAGNETIC uommem-mcJ' 4' FIG. 2

FIG. 3

mvsmons:

c. E. MURPHY, JR. M. M. PATTERSON a. c. SHEFFIELD THEIR ATTORNEY United States Patent 3,393,732 METHOD FOR LOCATING TENSION FAILURES IN OIL WELL CASINGS Carey E. Murphey, Jr., Maurice M. Patterson, and Bascom C. Sheffield, Houston, Tex., assignors to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed May 21, 1965, Ser. No. 457,606 3 Claims. (Cl. 1664) ABSTRACT OF THE DISCLOSURE A method for locating tension failures in a well casing caused by repeated heating and cooling of the casing. The tension failures are located by logging the well with a tool that is selectively responsive to a magnetic field and detecting the areas of increased magnetic field strength.

This invention pertains to a method for locating tension failures or the like in ferrous metal tubular members used as well casings. More particularly, the invention relates to a method for locating tension failures in the casing of a well in which the casing was heated and cooled, as, for example, the casing of a well used in a thermal recovery process.

In a steam soak thermal recovery process, steam is injected into a formation that contains a viscous crude oil. After the injection of a quantity of steam, the injection is stopped and the well is allowed to stand idle. After a given steam injection and soak period, the viscosity of the crude has been lowered by the action of the hot steam and the low viscosity crude may be produced. After a production period during which fluid inclusive of the low viscosity crude has been produced, the steam injection is again started and the cycle is repeated. In other thermal recovery processes it is often desirable to alter the subsurface flow pattern and convert a well through which hot fluids were injected or produced to one through which relatively cold fluids are produced or injected.

Wells that have been heated and then cooled, e.g., in a thermal recovery process such as a steam soak process of the type described above, have been subject to a high frequency of casing failures. It has been discovered that most of these failures are tension failures in which the casing breaks and the two sections separate. In addition, most of such breaks occur between and near the casing collars used for joining individual sections of the casing.

A principal object of the present invention is to provide a convenient and economical method for determining the existence and location of breaks in a ferrous metal casing string in a well.

A further object is to provide a practical method of determining the suitability of employing a selected extent of heating and cooling by flowing fluids in a well that has a given type of completion arrangement and extends through a given sequence of subsurface earth formations.

A further object is to provide a method of determining the existence and locations of breaks in a ferrous metal casing string by moving a measuring instrument through a tubing string disposed within the casing string.

The present invention is at least in part, based on a discovery that a break in a ferrou metal casing string that is installed in a generally vertical well is associated with a magnetic field which is materially stronger than the magnetic fields that are associated with collars, joints or other portions of tubing or casing strings that are contained in the well. Such a break may be due to a tension failure, in which the casing is pulled apart, or may be due to any failure that causes a relatively large gap in the magnetically permeable path that is formed by a ferrous metal conduit which extends more than a few hundreds of feet within the magnetic field of the earth.

In accordance with the present invention, the sensitivity of a magnetic field detecting means is adjusted to produce only a nominal response to magnetic fields associated with collars on a ferrous metal conduit disposed within a casing string of a Well, and the detecting means is moved through the section of the casing string which is to be inspected. The metal conduit within which the detecting means is moved can be either the casing string itself or a tubing string which is disposed within the casing string. The signal which is produced by the so-adjusted magnetic field detecting means when it is adjacent to a break in the casing string is significantly larger than and distinguishable from the signals which are produced when the detecting means is adjacent to the magnetic fields associated with collars or other anomalies in the metal conduit containing the detecting means.

Where the sensitivity of the magnetic field detecting means is adjusted so that a detectable, but nominal, signal is produced by the collars or other joints of the tubing or casing string containing the detecting means, the depths of the collars can be used to determine, or verify, the depth at which breaks are detected in the casing string. The depths of the collars on tubing or casing strings disposed within a well are known, or are readily determinable by methods known to those skilled in the art. Because of this, the present invention can be practiced by employing as a magnetic field detecting means a simple induction coil which produces an electrical signal that is proportional to both the strength of a magnetic field and the rate at which the coil is moved through the field. When such a coil is used, the means for recording inductions of the signals provided by the coil can comprise substantially any means for recording indications of the magnitudes of the electrical output in response to time and/or distance of the coil movement. In the use of such a coil, the coil and its associated recording equipment are preferably adjusted to provide a detectable, but nominal, indication when the coil is moved past a collar or joint at a selected rate, such as about 1 to 2 hundred feet per minute.

The present invention is uniquely advantageous for quickly locating tension failures in the casings of oil wells that have been used in thermal recovery operations. As mentioned above, it has been discovered that casing failures in wells that have been subjected to cyclic heating and cooling are likely to be tension failures that occur in the portion of the casing sections between the casing collars. It has further been discovered that it is ditficult to predict the extent of heating and cooling which is likely to cause such failures in the casing of a well that has a given type of completion arrangement and extends through a given series of subsurface strata. As known to those skilled in the art, the completion arrangements, i.e., the type of conduits such as casing strings, tubing strings, and their associated hanging, grouting, insulating, and the like equipment can be, and are, varied widely depending upon the economics of employing a given type of completion arrangement for the operations to be employed in a particular well. The stresses that are applied to a given casing string by given extent of heating and cooling are significantly affected by numerous factors. Such factors include the heat transfer properties of the fluids in the well, the heat transfer, reflectivity, and expansion, properties of both the cement or other grouting materials and the earth formations encountered by the well, the presence or absence of insulating materials, and the like factors.

Because of its capability of quickly locating tension failures, the present invention provides a practical method for determining the maximum extent of heating and cooling that should be employed in the operation of a well. This is done by operating a cased well that has the same type of completion arrangement and earth formation penetration for which information is desired. The selected well is tested by first flowing relatively 'hot, then relatively cool fluid through the well to provide an extent of cyclic heating and cooling that is being tested. The interior of the well is then traversed with a magnetic field detecting means that has a sensitivity providing only a nominal response to collars on the conduit containing the detecting means. The tests by identifying the conditions that cause failures indicate the extent of heating and cooling that should be employed in wells having the same type of completion arrangement and earth formation penetration as the tested well. The tested types of wells should only be employed in connection with an extent of heating and cooling that is less than amount that will cause responses to be produced that are significantly greater than those produced by the collars.

As used herein, the term collar is employed to refer to a thickened wall section and/ or collar associated with the joints of tubing or casing strings. Although such joints have numerous forms, they are all associated with thickened portions of metal. These thicker portions of metal are associated with magnetic fields which are typical of those associated with conventional casing collars. These thickened metal portions provide the zones of increased magnetizability which are responded to by collar locating devices, i.e., devices that are designed to provide a maximum signal output in response to such an increased concentration of magnetizable metal. The above objects and advantages of this invention will be more easily understood from the following detailed discussion of a preferred embodiment when taken with the attached drawing in which:

FIGURE 1 is an elevational view of an oil well casing showing a tool constructed according to this invention disposed therein and a block diagram form of the surface recording system;

FIGURE 2 is a vertical section of a downhole tool shown in FIGURE 1; and

FIGURE 3 is a typical recording obtained using the system shown in FIGURE 1.

Referring now to FIGURE 1, there is shown an oil well having a casing 9 disposed therein. The casing consists of a large number of individual sections that are joined together by casing collars. Portions of two sections 10 and 11 are shown joined together by a casing collar 12. Normally the ends of the sections contain male threads and the casing collar 12 contains female threads for joining the individual sections together. A tension failure or break 13 is illustrated in the section of the easing 11 adjacent the lower end of the collar 12.

Suspended in the casing by means of a cable is a magnetic field detecting means 14. The detecting means 14 may be of various designs. Suitable magnetic field detecting means include simple iron cored or core-free induction coils of the type shown in FIGURES 1 and 2, flux gates or rotating coil magnetometers, electron beams which are susceptible to deflection by magnetic fields, and the like devices that have a sensitivity capable of being adjusted to provide only a nominal response to the magnetic fields associated with collars on a metal conduit that is disposed within a casing string of a well.

The means shown in FIGURES 1 and 2 is a detector coil formed of a suflicient number of turns to generate a detectable but nominally sized signal when the coil is passed at about 200 ft. per minute through a magnetic field associated with a casing collar. The coil may be wound on a magnetizable core or a nonmagnetizable support means and in addition may be surrounded by magnetizable or nonmagnetizable materials. In addition, it is possible to use more than one coil and connect the coils in series to provide a larger signal. The cable 15 should have sufficient mechanical strength to support the probe 14 within the casing and, preferably, it should also have at least one electrical circuit for transmitting to the surface the electrical signal which is induced in the coil when the coil is moved through a magnetic field.

At the surface the cable 15 preferably passes over a measuring sheave which is connected to a Selsyn or a synchrogenerator unit 16. At the surface the electrical circuit in the cable 15 is coupled to an amplifier 17. The amplifier 17 amplifies the signal received from the coil in the magnetic probe 14 and supplies it via lead 20 to a recorder such as a pen chart recorder 26. The signal on the lead 20 is recorded as a trace 24 on the chart recorder. The chart paper of the recorder 26 is preferably driven in synchronism with the Selsyn unit 16 but can be driven at a selected time-base rate. The Selsyn unit 16 is coupled by means of a lead 27 to the chart recorder drive. A suitable recorder would be a model 299 recorder manufactured by the Sanborn Instrument Division of Hewlett- Packard.

The signals 31 and 32 on the record 24 illustrate signals that are induced in the magnetic coil of the magnetic probe when it passes a casing collar 12. The signal 33 illustrates the signal that is induced in the coil of the probe member when it passes the tension failure 13. The marks 36 recorded on the chart paper indicate equal intervals of travel of the probe 14 through the casing.

Referring to the above description, it is seen that in one embodiment of the invention an economical and easily operated probe member has been provided for detecting the presence of tension failures in oil well casings. More particularly, the probe consists essentially of an induction coil which requires no power to be supplied to the coil and only a single electrical circuit by which the signal is transmitted from the coil to the surface. The surface recording system records the presence of the tension failures and the locations of the casing collars. Thus, one may quickly locate the depths of the tension failure and check the accuracy of the depths by reference to the depths of the casing collars. As explained above, all of the tension failures are likely to occur between the casing collars.

Referring now to FIGURE 2, there is shown one embodiment of a probe member 14. The probe member consists of nonmagnetizable sections 40 and 41 disposed at opposite ends of the probe member. The magnetizable members 42 and 43 are disposed adjacent the coil member. The coil member consists of a magnetizable core member 44 having the coil winding 45 disposed thereon. The probe member is provided with a threaded connection 46 at its upper end to permit the attaching of a suitable cable connector to the probe. The leads from the coil 45 to the end cap are not shown in FIGURE .2.

The use of the magnetizable members 42 and 43 at the opposite ends of the coil member insure good magnetic coupling between the tubular casing and the core of the coil. By insuring good coupling a maximum signal will be induced in the coil 45 as it passes a tension failure in the casing. The dimensions of the probe member are preferably adjusted so that it can be lowered through conventional tubing strings such as 2-in. diameter tubing strings. The sensitivity of the probe member is preferably adjusted by selecting or altering the number of coil-turns and/or the core or pole piece arrangements in manners known to those skilled in the art, in order to provide a detectable, but nominal, response when the probe is moved through a tubing string and past a collar at a suitable rate. When such a probe is run through tubing, the tubing collars are demarked by signals such as those illustrated at 31 and 32 on FIGURE 1 and the signals due to the casing collars fail to appear, due to the rapid diminution of their magnetic fields with distance.

The capability of the present process, (1) to detect the existence and location of tension failures in well casings and (2) to determine to what extent heating and cooling should be employed in wells having a given type of well completion arrangement and formation penetration, has been demonstrated in field tests of the process.

In one such test the Well which was used contained 1,519 feet of 2%r-inch-EUE tubing hung within 8%-inch casing which extended through and was perforated within a reservoir interval. This well was logged to a depth of 1,400 feet by running a probe of the type shown in FIGURES 1 and 2 through the tubing string. The probe was run at a rate of about 200 feet per minute. The signals induced in the pickup coil were amplified at the surface and recorded on a Mosley x-y plotter having a built-in time base. The signal from the tool was recorded along the y axis versus time on the x axis. Depth was manually added, along the x axis at 100 feet intervals, from the visual indications on the cable truck depth counter. The resulting record is shown in FIGURE 3.

The regularly occurring small deflections of the FIGURE 3 record trace demark the tubing collars, and the large deflections near the depths of 500 and 950 feet, demark tension failures in the casing string. The average time which was required to run each of such logs in the fields in which these tests \were made was about 1 hour.

The fact that the deflections such as those shown on FIGURE 3 indicate the existence and location of tension failures in the casing was confirmed by pulling the tubing string of the logged well, filling the borehole with clear liquid, and visually observing the tension failures on the monitor screen of a television system for inspecting boreholes.

The well discussed above had been subjected to cyclic heating and cooling, resulting from an injection of steam at an average temperature of about 425 F. for about 2 weeks and producing fluids from the reservoir for a period of about 6 weeks. The above discussed detection of the tension failures in the casing string indicated the necessity of employing a more limited extent of heating and cooling in wells containing the tested type of completion arrangement and formation penetration.

In the same field, another well which encountered the same series of subsurface earth formations, but was completed with a different type of completion arrangement, was subjected to substantially the same extent of heating and cooling. The operations of this well were suspended long enough to run the above type of log. The absence of signals corresponding to magnetic fields significantly stronger than those associated with collars indicated the suitability of re-employing the same extent of heating and cooling in wells having that type of completion arrangement.

We claim as our invention:

1. A method for locating tension failures in a well casing, said method comprising:

moving through a casing a magnetism-responsive means that is selectively more responsive to a magnetic field than to a zone having a high concentration of magnetizable metal, and produces only a nominal response to magnetic fields associated with casing collars;

producing signals related to variations in the amount of magnetism that is encountered;

transmitting said signals to an indicating device; and indicating the magnitudes of said signals related to variations in the amount of magnetism in respect to the depth of said variations, wherein a break in the casing string is indicated by a signal which is significantly larger than and distinguishable from the signals related to the magnetic fields associated with casing collars. 2. A method of locating a tension failure in an oil well casing used in an oil well subject to repeated heating and cooling, said method comprising:

moving a magnetic search coil through said casing at a rate at which said coil produces signals related to variations in the amount of magnetism that is encountered and produces only nominal signals related to the magnetism associated with casing collars;

measuring the depth of said search coil in said casing;

transmitting said signals related to variations in the amounts of magnetism to the surface of the oil well;

recording said signals in relation to the depth of said search coil; and

indicating the depths at which said signals exceed and are located between signals due to collars. 3. A method for determining the extent of heating and cooling to be employed in the operation of the well, which method comprises:

operating a cased well that has a type of completion, and earth formation penetration that is being tested by first flowing relatively hot and then relatively cool fluid through the well to provide an extent of cyclic heating and cooling that is being tested;

traversing the interior of the well with a magnetic field detecting means having a sensitivity providing only a nominal response to collars on the conduit containing the detecting means;

repeating said relatively hot and cold fluid fiows with a difference in one of said relatively hot and cold fluid flows and then repeating said magnetic field detecting operation; and

employing in wells that have the tested type of completion arrangement and earth formation penetration only an extent of heating and cooling which is less than that which caused responses exceeding those due to collars to be produced by the magnetic field detecting means during said traversal of the interior of the tested well.

References Cited UNITED STATES PATENTS 2,228,623 1/1941 Ennis 166-4 2,246,542 6/ 1941 Smith 324-8 X 2,250,703 7/1941 Crites et al 324-34 X 2,553,350 5/1951 Bayhi 324-47 X 2,698,920 1/1955 Gieske 166-4 X 2,717,039 9/1955 Gieske 166-65 2,902,094 9/1959 Nelson et al. 166-4 X 3,091,733 5/1963 Fearon et al. 324-37 3,114,876 12/1963 Schuster 166-4 X 3,163,487 12/1964 Buck 324-34 X CHARLES E. OCONNELL, Primary Examiner.

I. A. CALVERT, Assistant Examiner. 

